Electrolyte balance in hypophysectomized goldfish, Carassius auratus L

Abstract

Hypophysectomized goldfish ( Carassius auratus L.) kept for 3 weeks in fresh water show a sharp decrease (35% or more) in plasma Na and Cl concentrations. Due to expansion of the apparent Na space, however, total exchangeable Na drops only about 20%. Flux analyses, using 22Na, show that hypophysectomized fish are in strongly negative Na balance. Urinary Na concentration rises but urine flow decreases to about 55% of normal. The rate of urinary Na loss is not significantly greater than that of intact or sham-operated fish. Negative Na balance is thus due to increased extrarenal Na loss. Repeated injections of sheep prolactin partially prevent the decline in plasma electrolyte concentrations. ACTH injections are ineffective in this respect. Survival of hypophysectomized goldfish in fresh water for long periods appears to be due largely to their ability to withstand dilution of the internal medium.